Abstract Medullary thyroid carcinoma (MTC) is a rare tumor with a current prevalence in the United States of 13,500 Americans. Advanced disease is mortal; patients with extra-cervical metastases have 5- and 10-year survival rates of 26% and 14%, respectively. After decades of limited effective available therapies, the Food and Drug Administration recently approved two new drugs, vandetanib (2011) and cabozantinib (2012), for the treatment of progressive, metastatic MTC; unfortunately, these drugs are not curative, response to therapy is not durable, and individual institutional and investigator experience remains limited due to the rarity of the disease. As a result, expert clinicians are left with unanswered questions regarding optimal drug use, and there continues to be a need for innovative drug research. Quality of life was not definitively studied as a goal of therapy in the trials for either drug, or little is known about how patients with advanced MTC make decisions regarding taking these newly-approved drugs and/or participating in clinical trials. The goal of this research is to describe the natural history of MTC via the utilization of a multi-institutional registry in order to understand the pathway to progressive disease requiring drug therapy, and integrating for the first time the patient perspective in order to identify patient reported outcome measures necessary to consider in current treatment and to include in clinical trial design. This data will inform emerging drug therapies for advanced MTC. This study will gather a comprehensive natural history to fully characterize the disease longitudinally from both the clinical and patient perspectives to identify demographic, clinical, pathologic, and genotypic predictors of progression to advanced MTC requiring approved drugs or enrollment in clinical trial, and patients? response to such therapy. Additionally, the study will characterize patients? experience with the progressive stages of MTC and treatment initiation through a systematic, longitudinal evaluation of patient-reported outcomes (PROs) that are relevant to the disease, including quality of life, symptoms and other outcomes.